Pumps of this type are well known and are referred to as Holweck pumps or as Gaede channel pumps. In pumps of this type, the rotor is in the form of a disk or a circular cylinder, or of a cone, and its surface is provided with at least one helical groove, while the facing surface of the stator is smooth, or alternatively, as is more commonly the case, it is on the contrary the surface of the rotor which is smooth and the surface of the stator which has grooves. Sometimes, both facing surfaces have such grooves. The depth of these grooves generally decreases going from the suction end to the delivery end.
In order to obtain good performance, it is important to reduce the operating clearance between the rotor and the stator to as small a value as possible, and this means that the rotor and the stator must be made very accurately. It is difficult to obtain very high accuracy in shape with prior art pumps.
German patent document number 912 007 describes a pump of this type but having a rotor which is spherical. This is most advantageous in that spherical surfaces can be made with very high accuracy, better than 1000th of a millimeter, by machining using a milling cutter or a cup wheel, or by molding, thereby reducing operating clearances.
The object of the present invention is to improve a pump of this type by increasing its compression ratio.